Download Marine Ecoregions of North America

Attu
Point Hope
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1.1.3
1.2
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1.3
1.1.2
1.1
Hooper Bay
1.1.1
1.2
1.1.3
1.1.1
False Pass
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400 km
Anchorage
Kodiak
1. Bering Sea
Level II seafloor geomorphological regions include:
1.1
1.2
1.3
Bering Shelf
Bering Slope and Bowers Ridge
Bering Basin
Level III coastal regions include:
1.1.1
1.1.2
1.1.3
Bristol Bay and Kuskokwim Bay
Norton Sound
Middle and Outer Bering Sea Neritic
Regional Overview
The Bering Sea is the world’s third-largest, semi-enclosed body
of water. Noted in particular for its wide coastal shelf and high
productivity, the Bering Sea Ecoregion is of special conservation
importance to marine mammals and fisheries, and is a unique
subpolar ecosystem. It is bounded by the Bering Strait in the
north and the arc of the Aleutian Island chain to the south, and
divided in half physiographically, with a broad shelf to the east
and much deeper oceanic plains to the west.
The Bering Sea Region includes two B2B6 Marine Priority Conservation Areas (PCAs): PCA 1-Pribilof Islands, and PCA 2-Bristol
Bay (Morgan et al. 2005).
Physical and Oceanographic Setting
The Bering Sea Ecoregion includes a broad eastern shelf, gently
sloping for the first 100 m and then descending at a slightly
steeper rate to the shelf edge at around 200 m. The continental
6 As noted by Morgan and others (2005), “a total of 28 sites were identified as PCAs, spanning seven marine ecoregions in the B2B region,
totaling eight percent of the total EEZ area of the three nations.” PCAs for the Arctic and Atlantic Oceans and the Caribbean Sea
have not as yet been identified. For further information on the process and the regions identified, see Morgan, L., S. Maxwell, F. Tsao,
T.A.C. Wilkinson and P. Etnoyer. 2005. Marine Priority Conservation Areas: Baja California to the Bering Sea. Montreal: CEC and MCBI.
slope is incised with many canyons and drops to a generally flat
abyssal plain, 3,700–4,000 m deep. Major islands on the shelf are
the St. Lawrence and Nunivak Islands (which are the largest in
the Bering Sea), the Pribilofs (Fur Seal Islands), and St. Matthew,
Nelson, and Karagin Islands. Currents in the Eastern Bering Sea
flow in a generally counter-clockwise direction, with an Aleutian
North Slope Current flowing northeast along the inside of the
Aleutian Island chain and curving northwest at the shelf edge to
form the Bering Slope Current. A northeast drift current flows
along the coast over the nearshore shelf. Net circulation flow
is from the Bering Sea to the Chukchi Sea through the Bering
Strait. The annual formation and retreat of sea ice through the
Bering Strait and out over the northeast shelf is a major determinant of the distribution of many species. The Yukon River is the
largest river flowing into the eastern Bering Sea.
Biological Setting
The Bering Sea is among the most productive of high-latitude
seas, supporting a large biomass of fishes, birds and marine mammals. The southeast Bering Sea contains two fairly distinct uppertrophic level species groups, or guilds, based on characteristics of
feeding. The first group consists of an outer shelf pelagic group of
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Fact Sheet
Rationale: defined by sea surface temperature and the semi-enclosed physiography of the sea Surface: 1,468,220 km2
Sea surface temperature: Avg. <2°C (winter), 6°–14°C (summer)
Major currents and gyres: dominated by tidal flows. A counter-clockwise Aleutian North Slope
Current and Bering Slope Current flow along the north edge of the Aleutians and west edge of the
Bering Shelf respectively. The major direction of flow is northward through the Bering Strait.
Physiography: The wide coastal shelf is bounded by the Aleutian Island chain to the south
and the Bering Strait to the north.
Depths: shelf (roughly 0–200 m): 51%7; slope (roughly 200–2,500/3,000 m): 14%; abyssal plain
(roughly 3,000+ m): 35%
Substrate type: generally muddy sand and gravel
Major community types and subtypes: seasonal sea ice, high productivity pelagic systems,
polar and subpolar communities
Productivity: moderately high (150–300 g C/m2/yr)
Species at risk: bowhead whale, blue whale, fin whale, gray whale, North Pacific right whale,
Pacific walrus, Steller sea lion, northern fur seal, short-tailed albatross, red-legged kittiwake, Steller’s eider, king eider
Human activities and impacts: commercial and subsistence fishing and hunting, oil exploration
and recovery
7 Percentages found in the fact sheet and following text are approximate. There are some cases where totals
amount to 99 or 101 percent. This is due to the addition of rounded (up or down) percentages.
fish, mammals and birds that consume small fish—primarily juvenile pollock, and krill. The second group is an inshore group of
fish, crabs and other bottom dwelling fauna that consume mainly
benthic infauna. In the outer shelf, walleye pollock dominate the
biomass and represent a keystone species in the system. Springer
(1996) determined that juvenile walleye pollock are important
prey for seabirds during the nesting season. In addition, Lowry
et al. (1996) found that all species of phocid seals feed on walleye
pollock, with the species predominating the diets of harbor, spotted
and ribbon seals.
Many species move seasonally with the advance and retreat of
sea ice, including many fishes, walrus and seals. Summer residents consist of species that feed and reproduce in the region,
such as northern fur seal, Steller sea lion, and seabirds such as
murres, black-legged kittiwakes, and auklets, as well as species
that use the area to feed but reproduce elsewhere—including fin
whale, the eastern North Pacific stock of gray whale and oceanic
seabirds, especially shearwaters.
The region is particularly important for marine mammals—
especially the rare Steller sea lion. The western Alaskan stocks
Crested and least auklets nest on island coasts such as those of the Aleutian Islands in the Bering Sea. © Nikolay Konyikhov/AccentAlaska.com
12 Marine Ecoregions of North America
of Steller sea lion have undergone a continuous decline since
the 1970s—they were listed as a threatened species under the
US Endangered Species Act in 1990, then declared endangered
in 1997. Management measures, including buffer zones around
rookeries and alternatives to mitigate potential impacts of
commercial fisheries on important prey species, are presently
being developed.
Over the last decade, significant changes have occurred in the
Bering Sea, possibly due to shifts in the Pacific Decadal Oscillation and Arctic Oscillation. The character of the seasonal ice
pack recently has changed from the “warm” phase that persisted
since the regime shift of the late 1970s to one that exhibits rapid
buildup in winter but earlier retreat in spring. The timing of
spring primary production is determined predominately by the
timing of ice retreat. The distribution and abundance of pollock,
Pacific cod and other commercially important fishes have varied
with these fluctuations in sea ice, and the ability of these fish
populations to withstand fishing pressure is expected to vary
between warm and cold regimes (Hunt et al. 2002).
Human Activities and Impacts
Several small towns and numerous Alaskan native villages
sparsely populate the Alaskan coast of the Bering Sea. Subsistence use of coastal resources in the region includes nearshore
harvesting of salmon and other fishes, invertebrates and marine
mammals, including seals, Steller sea lion, Pacific walrus and
polar bear. Subsistence hunting of the northern fur seal on the
Pribilof Islands is limited by quota and other regulations as the
species has been listed as depleted in the US Marine Mammal
Protection Act. Offshore, commercial fisheries in the region are
of major importance—Bering Sea fish and shellfish constitute
almost 5 percent of the world and 40 percent of the US fisheries harvest (Macklin 1999). Pollock, salmon, Pacific halibut and
crab generate over US$2 billion each year in fisheries revenue
and provide a major source of protein. At present, some Bering
Sea fisheries, such as pollock, have experienced major changes
in abundance over the last thirty years, although they appear
not to be overexploited. Populations of several species, such as
king crab and Greenland halibut, however, are at near historical
lows. In addition to fishing and hunting, oil and gas exploration
and recovery activities are prevalent in the region. Ecological
conditions of the coastal resources in Alaska are poorly known.
Alaska has assessed less than 0.1 percent of its coastal estuaries
(EPA 2005). In the US northern Pacific and western arctic ecoregions (1, 2, 22 and 23) two out of 35 federally fished stocks are
overfished (NMFS 2007).
Adult red-legged kittiwake at nest. One of the largest colonies of this species, currently at risk, is in the Pribilof Islands.
© Nikolay Konyikhov/AccentAlaska.com
Bering Sea
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Male Pacific walrus haul out on the rocky shores of Round Island, Alaska, to rest and sunbathe. Photo: Tom Bledsoe/DRK PHOTO